Slew rate limited reference for a buck converter
a reference voltage and converter technology, applied in the direction of electric variable regulation, process and machine control, instruments, etc., can solve the problems of limited reference voltage, unsuitable, passive drooping,
Inactive Publication Date: 2005-03-22
ANALOG DEVICES INC
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- Application Information
AI Technical Summary
Benefits of technology
The solution effectively limits the rate of change in output current, corrects for voltage drops in ground traces, and improves accuracy by controlling the slew rate and reducing offset errors, enhancing the stability and precision of the buck converter's response to load changes and VID programming.
Problems solved by technology
In one case, the slew rate of the reference voltage is limited after power is turned on with a soft start capacitor.
This may not be desirable because of the high currents that result every time a VID transition occurs.
The other problem with most CPU power supply controllers is the previously discussed passive droop.
The feedback voltage (sensing voltage) for the power supply controller generally cannot be taken directly at the output close to the output filter capacitors because of stability concerns.
The stability concerns are caused by the low equivalent series resistance (ESR) of the network of parallel ceramic capacitors used for the output filter.
Since load current flows through the PCB traces, any resistance resulting from sensing upstream results in a voltage drop.
Since this resulting voltage drop is not inside the feedback loop, the controller cannot correct for these voltage drops.
The output voltage droops as a fiction of load current creating a load regulation error.
Sometimes this load regulation error is desirable, however, because the PCB trace resistance is unpredictable this may not be the best way to introduce intentional voltage droop.
Passive droop may also result from a difference in ground potentials for different circuits.
This is especially true in high current applications where the voltage drop in PCB traces may be significant.
However, it is not always possible to locate the bandgap reference 119 and reference DAC 115 close to Vout 120.
Method used
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In the following description, numerous specific details are set forth to provide a thorough understanding of the present invention. However, it will be obvious to those skilled in the art that the present invention may be practiced without such specific details. In other instances, well-known circuits may be shown in block diagram form in order not to obscure the present invention in unnecessary detail. For the most part, details concerning timing considerations and the like have been omitted in as much as such details are not necessary to obtain a complete understanding of the present invention and are within the skills of persons of ordinary skill in the relevant art.
Refer now to the drawings wherein depicted elements are not necessarily shown to scale and wherein like or similar elements are designated by the same reference numeral through the several views. The term “buck converter” is used herein to describe the broad class of DC-to-DC converters that have a regulator input vol...
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A compensated reference voltage for the controller of a buck regulator corrects for offsets and controls the rate at which the output load current can change in response to a change in the reference setting output voltage level of the buck converter. A current source is coupled to a resistor that has one terminal connected to the ground potential of the output voltage. The voltage across this resistor generates a remote reference voltage. A feedback current is generated as a function of the difference between the remote reference voltage and the output voltage. The feedback current is time integrated to form the compensated reference, which is used to control the ON-time of the buck converter.
Description
TECHNICAL FIELDThe present invention relates in general to controllers for switching regulators and in particular to controllers that set a relatively constant ON-time for the switching devices in switching regulators.BACKGROUND INFORMATIONIn some applications a buck controller is used in the power supply for a central processing unit (CPU). Most modern CPU integrated circuits (ICs) use some form of voltage control to regulate power dissipation; the CPU's voltage is lowered to conserve power and increased when higher performance is desired. The CPU may signal the power supply controller by supplying a voltage identification (VID) setting indicating a desired power supply voltage. In a buck regulated power supply, the buck controllers must control the output voltage in response to a change in VID settings. Many buck controllers rely on a current limit to control the maximum output current in response to a new VID setting. Other buck controllers use a digital up / down counter to slew t...
Claims
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IPC IPC(8): H02M3/04H02M3/156
CPCH02M3/156H02M2001/0025H02M1/0025
InventorPULLEN, STUARTGROOM, TERRY J.
OwnerANALOG DEVICES INC